I figured the ban was pointless because most places that serve fountain drinks give free refills, so it doesn't matter if the container is 2oz as long as you can refill it. Also, nanny state etc.
But my girlfriend (who happens to [sort of] work for the mayor) pointed out that it's essentially like raising taxes on cigarettes; if you insist on doing something that is bad for you, you'll have to pay more for it. And, in the soda case, it'll spark a larger conversation about portion control/size, etc. which most people are clueless about. So, I'm marginally for it I suppose. I barely drink any soda so it doesn't make a personal difference to me.